Over time and through repeated use, bones and joints can become damaged or worn. For example, repetitive strain on bones and joints (e.g., through athletic activity), traumatic events, and certain diseases (e.g., arthritis) can cause cartilage in joint areas, which normally provides a cushioning effect, to wear down. When the cartilage wears down, fluid can accumulate in the joint areas, resulting in pain, stiffness, and decreased mobility.
Arthroplasty procedures can be used to repair damaged joints. During a typical arthroplasty procedure, an arthritic or otherwise dysfunctional joint can be remodeled or realigned, or an implant can be implanted into the damaged region. Arthroplasty procedures may take place in any of a number of different regions of the body, such as a knee, a hip, a shoulder, or an elbow.
One type of arthroplasty procedure is a total knee arthroplasty (TKA), in which a damaged knee joint is replaced with prosthetic implants. The knee joint may have been damaged by, for example, arthritis (e.g., severe osteoarthritis or degenerative arthritis), trauma, or a rare destructive joint disease. During a TKA procedure, a damaged portion in the distal region of the femur may be removed and replaced with a metal shell, and a damaged portion in the proximal region of the tibia may be removed and replaced with a channeled piece of plastic having a metal stem. In some TKA procedures, a plastic button may also be added under the surface of the patella, depending on the condition of the patella.
Accuracy in implant alignment is an important factor to the success of a TKA procedure. A one- to two-millimeter translational misalignment, or a one- to two-degree rotational misalignment, may result in imbalanced ligaments, and may thereby significantly affect the outcome of the TKA procedure. For example, implant misalignment may result in intolerable post-surgery pain, and also may prevent the patient from having full leg extension and stable leg flexion.
Preoperative planning may be used prior to some TKA procedures to help determine where to position an implant and how to align the implant. Certain preoperative planning methods may include making these determinations based on a two-dimensional image of the target site. In some cases, though, the two-dimensional image may not provide sufficient guidance for precisely replacing a patient's diseased knee with an implant. For example, a physician may rely on certain landmarks of the target site, as shown in the two-dimensional image, for determining placement of an implant. Examples of knee region landmarks that may be relatively easily viewed in a two-dimensional image include the medial and lateral epicondyles of the distal region of the femur. However, the corresponding bone regions in the body typically are covered with soft tissue. This soft tissue may cause the landmarks to be partially obscured or completely hidden when the physician is trying to position an implant at the target site, and may make it especially difficult to view the landmarks when the physician is using a relatively small incision. Moreover, using such landmarks to position an implant at a target site may have added difficulty in that the locations and sizes of the landmarks can vary greatly from one patient to another. As a result, a landmark-based technique that is used for one patient may not be suitable for use with another patient. For at least the reasons provided above, a physician using a landmark-based approach may experience difficulty during surgery, such as difficulty in accessing the rotational axis. Because of this difficulty, many surgeons opt to rely significantly on their intuition and previous experience to guide them in a TKA procedure. The result can be inconsistent surgical outcomes, given the highly complex nature of the human knee, with its six degrees of freedom and features, such as dimensions and alignment, that can vary greatly from one patient to the next.
In certain TKA surgeries, a robot is employed to machine the distal region of the femur and/or the proximal region of the tibia based on, for example, image-based preoperative planning. The robot may form cavities that may be used for attachment of prosthetic implants. While robot-assisted TKA procedures may be successful in terms of accuracy of alignment, they can require relatively long incisions and result in relatively long surgery times. Furthermore, the cost of a robot-assisted TKA procedure, including the capital cost, can be relatively high (e.g., two to three times the cost of a traditional TKA procedure).
In some TKA surgeries, an imageless navigation system is employed, in which planning is done intraoperatively (i.e., during the operation), without the use of preoperative radiographic images. The navigation system can assist surgeons in positioning prosthetic implants, and may thereby enhance the longevity of the implants. However, the navigation system may not provide information regarding the optimal alignment of an implant. Furthermore, the capital equipment cost associated with a navigation system can be relatively high, and the use of a navigation system may result in a longer incision, a higher surgical cost, and a longer duration of surgery, as compared to traditional surgery.
Implants that are implanted into a damaged region may provide support and structure to the damaged region, and may help to restore the damaged region, thereby enhancing its functionality. Prior to implantation of an implant in a damaged region, the damaged region may be prepared to receive the implant. For example, in a knee arthroplasty procedure, one or more of the bones in the knee area, such as the femur and/or the tibia, may be treated (e.g., cut, drilled, reamed, and/or resurfaced) to provide one or more surfaces that can align with the implant and thereby accommodate the implant. However, prior to treating any regions of a bone, it is important to correctly determine the location at which the treatment will take place. In some methods, an arthroplasty jig may be used to accurately position a finishing instrument, such as a cutting, drilling, reaming, or resurfacing instrument. The arthroplasty jig may, for example, include one or more apertures and/or slots that are configured to accept such an instrument.
A relatively high number of arthroplasty procedures are performed every year in the United States, and throughout the rest of the world. More specifically, in the United States alone, more than 300,000 people underwent TKA surgeries in 2005. By 2008, it is expected that approximately 1,000,000 people per year across the globe will have a TKA surgery. Accordingly, it would be desirable to improve the success rate of arthroplasty procedures, in terms of both efficiency and effectiveness. It would also be desirable to be able to meet demand for arthroplasty devices by manufacturing arthroplasty jigs and/or implants, including customized arthroplasty jigs and/or implants, relatively efficiently.